Data storage devices are commonly used to store data in computers, data bases, digital video recorders, and other devices. Data storage devices may include hard disks, solid state memory, or other types of memory.
FIG. 1 shows a prior art disk drive 110 comprising a rotating magnetic disk 115 and a head 120 connected to the distal end of an actuator arm 125, which is rotated about a pivot by a voice coil motor (VCM) 130 to position the head 120 radially over the disk 115. The disk 115 comprises a number of concentric data tracks 140, each partitioned into a number of data sectors. To write data to the disk 115, write circuitry 145 positions the head 120 over a target data track using the VCM 130 and sends the data to the head 120. The head 120 magnetically writes the data to the disk 115 when the head 120 is positioned over a desired data sector of the target data track during rotation of the disk 115.
Disturbances in the disk drive 110, such as vibration and physical shock, are becoming an increasing problem as the number of tracks per inch (TPI) is increased for higher storage capacity. For example, disturbances can cause the head 120 to deviate from the target data track and overwrite a neighboring data track, resulting in a loss of data on the disk 115. To compensate for disturbances, a disk drive 110 may employ an adaptive compensation scheme that detects disturbances using one or more sensors and compensates for the detected disturbances by repositioning the head 120 based on the detected disturbances to keep the head 120 within the target data track.
When compensation is not enough, the disk drive 110 may include a shock sensing circuit 150 that detects certain shock events and a controller 155 that instructs the write circuitry 145 to abort a write operation when a shock event above a certain threshold is detected to prevent off track writing and protect the data on the disk 115. The shock events may include drive/chassis thermal popping and notebook disturbances such as typing, taping and cover-closing, which may exceed the shock specifications of the disk drive in frequency range and/or amplitude. The thermal popping is caused by dissimilar coefficients of thermal expansion among different components inside and outside of the disk drive 110.
Increasing the sensitivity of the shock sensing circuit 150 makes the disk drive 110 more robust against shocks. However, if the shock sensing circuit 150 is tuned to be too sensitive, then a high disturbance environment (e.g., vibrations, power noise, E/B field noise, etc.) can trigger the shock sensing circuit 150 so much that drive performance is reduced to unacceptable levels. This is because, each time the shock sensing circuit 150 is triggered, a scheduled write operation is aborted and delayed until the detected shock passes. As a result, a high rate of shock detections can degrade the data throughput performance of the disk drive 110.
Accordingly, there is a need for adaptive shock detection that provides protection from shock events while maintaining good data throughput performance.